GitLab

This change follows this proposed behaviour:

 Ctrl+Shift+Left:  move to last visited directory
 Ctrl+Shift+Right: move to next visited directory

an alternative behaviour would be:

 Ctrl+Shift+Left:  move directory to the left in `dirs` output
 Ctrl+Shift+Right: move directory to the right in `dirs` output

It also introduces `setopt nopushdminus` as a way to standardise
pushd syntax. It's value wasn't clear before, which has been the
cause of so many pull requests regarding this plugin not working
in some environments.

dircycle right did not behave as expected and was fixed